Drill hole type cathode with cooling means



P 7, 1965 B. P. DE LANY ETAL 3,205,388

DRILL HOLE TYPE CATHODE WITH COOLING MEANS Filed Dec. 30, 1960 2Sheets-Sheet 1 z l 54 f 1 0/1298 A A Sbdrce l INVENTORS.

par/kw" Z far/er lf/far/feyz p 1965 a. P. DE LANY ETAL 3,205,388

DRILL HOLE TYPE GATHODE WITH COOLING MEANS Filed Dec. 30, 1960- 2Sheets-Sheet 2 IN V EN TORE from the nearest part of the cathode.

United States Patent 3,205,388 DRILL HOLE TYPE CATHODE WITH COOLINGMEANS Beatrice Pearson De Larry, 36 La Gorce Circle, Miami Beach, Fla.,and Paul L. Copeland, 17 W. 80 Oak Lane,

Bensenville, Ill.

Filed Dec. 30, 196i), Ser. No. 7%,836

7 Claims. (Cl. 313-35 This invention relates to gas discharge tubes andin particular to improvements in the cathode of said tubes.

A primary purpose of the present invention is to provide a means forselectively cooling the cathode hole of a gas discharge tube to improvethe operation of the discharge.

A further purpose is to provide an electric discharge tube of the gastype wherein the cathode has an elongated hole which is cooled toincrease the density of the gas within it.

Another purpose is to provide a tube of the type described havingincreased stability of the are or glow at low-current densities.

Another purpose is to provide a means for selectively cooling thecathode in an electric discharge tube of the type described.

Another purpose is to provide an improved voltage regulator tube of thetype described,

Other purposes will appear in the ensuing specification, drawings andclaims.

The invention is illustrated diagrammatically in the following drawingswherein:

FIGURE 1 is a longitudinal section through a gas discharge tube of thetype described showing one means for cooling the cathode,

FIGURE 2 is a section, similar to FIGURE 1, showing a further means forcooling the cathode,

FIGURE 3 is a longitudinal section showing a variant form of gas typedischarge tube and yet a further means for cooling the cathode,

FIGURE 4 is a section along plane 4-4 of FIGURE 3,

FIGURE 5 is a partial section showing a further means for cooling thecathode, and

FIGURE 6 is a schematic illustration of the tube of this invention in avoltage regulator circuit.

If a drill hole with its diameter suitably related to the mean-free-pathof electrons in the gas is present in the cathode of a glow discharge,the discharge at the cathode will be confined almost entirely to theinterior of said hole. In the glow discharge electrons are emitted fromthe cathode as a result of any of several processes in the discharge.

These electrons are immediately accelerated in the cathode fall ofpotential. There is some chance that -an electron will ionize a moleculeof the gas either near the end of the cathode fall or in the luminousgas which marks the beginning of the less rapid potential variation. Ifan electron in the drill hole, however, has not lost its energy inelastic impacts with gas molecules by the time it enters the cathodefall diametrically across from its point of origin, it again traversesnearly the entire cathode fall and is slowed down in the process. Itspotential energy, however, has increased, and after being brought torest for an instant, it is again accelerated away As it acquires kineticenergy, it becomes able to ionize the gas molecules. In this way it mayoscillate back and forth between diametrically opposite sections of thecircumference of the cathode hole until it has lost a large part of itsenergy in the production of ions. The concentration of electrons movingthrough the hole space during any period of time is thus greatlyincreased. The potential difference across the discharge is reduced whenit operates in this Way, and the drill hole is so effective that thedischarge often concentrates within it, leaving other more exposedportions of the cathode structure dark,

The effectiveness of a drill hole in the cathode of an electricaldischarge device at a given pressure of gas depends upon the temperatureof the walls of the drill hole. To increase the effectiveness of thecathode, the material should be cooled. In other words, the cathodeshould be selectively cooled, as obviously to cool the entire tube isnot useful, because it merely reduces the pressure without a significantincrease in the concentration of molecules within the drill hole.According to the general gas laws an increase in pressure and decreasein temperature give rise to effects in the same sense. In other words,according to the general formula PV=RT, either an increase in pressureat constant temperature or a decrease in temperature at constantpressure will increase the density of the gas. As in many applicationsit is not practical to increase the amount of gas in the tube, it istherefore necessary to provide a method of cooling the cathode in orderto increase the density of the gas within the cathode hole. Accordingly,it is the primary purpose of this invention to provide a gas typedischarge tube utilizing a cathode hole with means for cooling thecathode hole to increase the density of the gas Within the hole.

In FIGURE 1, a gas impervious envelope 10, which may be a glass envelopeas conventional, encloses an anode 12 having a lead-in wire 14. Thespace Within the envelope 10 may be filled with an inert gas, forexamples helium or argon, or any one of a number of suitable gases. Atthe end of the envelope 10 opposite the anode 12 is a cathode 16 in theform of an elongated rod or bar having a longitudinal bore or hole 18.The bore or hole faces 01' opens into the interior of the tube and maybe axially aligned with the anode 12. A lead-in 20 supplies the electricconnection for the cathode. The cathode 16 may have a shell consistingof copper sealed to the glass of the tube in a conventional housekeeperseal shown attached to the envelope 10 at 22, or it may have itsexterior formed of one of the alloys which is chosen to have anexpansion coefiicient matching that of the glass to which it is sealed.The drill hole itself may be in a slug of material which is fitted intothe metallic shell completing the envelope. This slug may be of mischmetal or one of its purified components such as cerium, or it may be ofbarium or strontium. A material of low work function is desirable forthe interior surface of the drill hole, and cesium or another of thealkali metals may be used in a film coating the interior surface of thedrill hole.

In the form of the invention shown in FIGURE 1, the cathode isselectively cooled by placing the body of the cathode outside of theenvelope 10. In other words, the cathode body 16 will be surrounded byair at atmospheric pressure and temperatures so that the heat of thecathode will be dissipated to the surrounded volume.

In FIGURE 2, an air impervious envelope 24 encloses an anode 26 having alead-in wire 28. In this form of the invention, the cathode includes acathode body 30 formed similarly to the cathode body 16 of FIGURE 1 andincluding a drill hole or bore 32 opening into the interior of the tube24, and again generally axially aligned with the anode 26. The envelope24 extends toward and along the cathode 30 to define a cup-like area 34around the cathode 30. This cup-like area 34 may hold a suitable coolingmedium, for example water, ice or solid carbon dioxide. Any one of thesematerials is satisfactory'for dissipating the heat of the cathode.Preferably, the out side of the cathode and the bottom 36 of thecup-like area 34 is formed of copper. Again there is a conventionalhousekeeper seal between the copper plate and the glass tube 24.

In the structure shown in FIGURE 2 the heat genertube envelope.

ated by the cathode is dissipated through the cooling medium placed inthe cup-like area 34 to accordingly cool the drill hole within thecathode 30.

FIGURE 5 shows a modification of FIGURE 2 in which a spiral coil 23passes around the cathode 30. The coil may have an inlet 25 and anoutlet 27 and, may carry any suitable coolant. A continuouslycirculating coolant is quite efficient in cooling the drill hole.

A further form of the invention, shown in FIGURE 4, is utilized with atube having an identical element at each end. Such a tube may be usedwith alternating current and each element alternately serves as thecathode of the tube. An air impervious envelope 38, encloses twoidentical elements 40 each of which are composed of a central elongatedbody 42 having an axial or longitudinal bore or hole 44 and a pluralityof radially extending fins 46. A lead-in48 is used as the electricalconnection between the element within the tube and the circuit.

In this form of the invention, the radially extended fins 46 provide ameans for dissipating the heat of the cathode, or in effect, cooling thecathode drill hole. FIGURE 6 shows one use of the tube described herein.When the tube 50 is positioned in parallel with a load 52 and a source54 it provides an excellent voltage regulator.

The use, operation and function of the invention are as follows:

This invention relates to electrical discharge in gases, and it providesa means of stabilizing the glow. An elongated cathode member having aso-called drill hole extending longitudinally or axially of the cathodemay be used. The use of such a cathode hole initially stabilizes theglow within it even at low currents. It has been observed, however, thatafter operating a tube of this type for some time, particularly at highcurrents, the discharge may go out entirely when the current is reduced;or, due to the heating of the cathode, the concentration within thedrill hole may be eliminated and the form of the discharge may be soradically altered that the device does not have characteristics suitablefor the application attempted. A primary purpose of the presentinvention is to stabilize the form of the discharge between the cathodeand the anode and to produce steady operation.

The particular tubes shown and described herein have an extremely widerange of application. They may be .used as sources of light and areespecially suitable if a concentrated source is desired. They may alsobe used for achieving particular spectral characteristics of the light.'Circuit applications of these tubes may also be made. A particularapplication of this tube has been found in volt- ..age regulatorcircuits. .the type described can supply excellent voltage regula- Ithas been found that a tube of metal is however preferred for the cathodealthough cesium or any one of the rare earth or alkali earth metals arealso satisfactory. A number of different elements may be used in thecathode formation and it is not intended to restrict the invention toany single material. The same is true of the'particular gas placedwithin the Helium is satisfactory as is nitrogen or any one of the noblegases, as the only requirement is that the gas be inert chemically.

The pressures 'of the gas within the tube may vary Widely and in generalit may be said that the pressures are lower than those conventionallyused in electric discharge tubes. With drill holes of nearly an inch indiameter we have used inert gas pressures on the, order of 100 micronsof mercury. The pressures as previously noted depend on the diameter ofthe drill hole and for "wire size" drill holes, Five microns of mercuryproved a satisfactory pressure. The size of the hole will vary accordingto the particular size of the tube, however hole diameters in the rangeof of an inch to of an inch are satisfactory. As an example, if the holehas a inch diameter, it should be approximately 11 inches long, asalthough the exact dimensions are not critical, the relative dimensionsare. For example, the ratio of hole diameter to hole length should neverbe less than 1:10. The hole must be long in order to provide theincreased stability and range of current variation required.

The advantage of the cathode hole lies in the fact that the restrictedarea of the hole provides for a concentration of gas molecules within anarea which is crisscrossed by heavy electron movement, thussubstantially increasing the possibility of ionizing the gas molecules.In other words, the radial distance traversed by an electron as it movesfrom one wall of the drill hole to another is small so that theelectrons rapidly move back and forth until they have an inelasticimpact with a gas molecule, thus producing ionization. It has beendiscovered that ionization can be further increased by increasing thedensity of the gas or the number of molecules per cubic centimeterwithin the cathode hole. Accordingly, to increase the number ofmolecules within the cathode hole it is necessary either to selectivelydecrease the temperature of the hole or to increase the pressure. Inmost applications, it is impractical to increase the pressure by addingmore gas, therefore it is necessary to decrease the temperature of thedrill hole itself. The only way to decrease the temperature is to coolthe cathode body. Accordingly, shown and described herein are fourdifferent methods of cooling the cathode.

In FIGURE 1, the body of the cathode is positioned outside of the tubeenvelope, although effectively within the tube, so that the heat of thecathode may be transferred by conduction to the surrounding atmosphere.In FIGURE 2, the cathode is not enclosed within the envelope, and has acold storage cup-like volume around the cathode. The cup-like volume maycontain any one of a number of satisfactory cooling substances. In FIG-URE 3, the cathode is cooled through the use of radially extending finswhich will dissipate the heat of the cathode'to other portions of thetube. In FIGURE 5, a coolant coil passes around the cathode.

The increased ionization and hence increased stability of the dischargeat low-current densities, as stated above, is caused by cooling thecathode hole. Cooling the cathode relative to the other parts of theenclosed volume increases the concentration of molecules withinthecathode hole and also prevents the loss of ions by diffusion. Bothresults lead to increased efficiency of the tube. In addition, coolingthe cathode will keep the cathode from disintegrating. As the cathodeheats up and reaches high temperatures during operation, it is likely topartially disintegrate. Accordingly, cooling the cathode reduces thecathode disintegration and thus increases the life of the tube.

Whereas the preferred form of the invention has been shown and describedherein, it should be realized that there are many modifications,substitutions and alterations thereto within the scope of the followingclaims.

We claim:

1. An electric discharge tube including an air impervious envelopefilled with an inert gas at a pressure between microns and 5 microns ofmercury, an anode positioned within said envelope and a lead-in for saidanode, an elongated solid metallic cathode positioned opposite and awayfrom said anode and arranged to provide an electric dischargetherebetween, a lead-in for said cathode, a longitudinal elongated holein said cathode generally in alignment with said anode, and means forselectively cooling said cathode to stabilize the discharge between thecathode and anode and to increase the gas density within the hole.

2. The structure of claim 1 further characterized in that the means forselectively cooling said cathode in clude a plurality of outwardlyextending fins positioned upon and around the periphery of said cathodeand within said envelope.

3. The structure of claim 1 further characterized in that the body ofsaid cathode is outside of said envelope with the hole opening into theinterior of said envelope.

4. The structure of claim 1 further characterized in that the body ofsaid cathode is outside of said envelope with the hole opening into theinterior of said envelope, and means for maintaining a cooling mediumaround the body of said cathode.

5. An electric discharge tube including an air impervious envelopefilled with an inert gas, an anode positioned within said envelope and alead-in for said anode, an elongated solid metallic cathode positionedopposite and away from said anode and arranged to provide an electricdischarge therebetween, a lead-in for said cathode, a longitudinalelongated hole in said cathode generally in alignment with said anode,the ratio of length to width of said cathode hole being at least :1 andthe hole being round in cross section.

6. An electric discharge tube including an air impervious envelopefilled with an inert gas, an anode positioned within said envelope and alead-in for said anode, an elongated solid metallic cathode positionedopposite and away from said anode and arranged to provide an electricdischarge therebetween, a lead-in for said cathode, a longitudinalelongated hole in said cathode generally in alignment with said anode,the body of said cathode being outside of said envelope with the holeopening into the interior of said envelope, and means for maintaining acooling medium around the body of said cathode to stabilize thedischarge between the cathode and anode and to increase the gas densitywithin the hole, including an extension of said air impervious envelopeforming a cup-like volume around said cathode, with the cathode beinggenerally in the center of said cup-like volume.

7. An electric discharge tube including an air impervious envelopefilled with an inert gas, an anode positioned within said envelope and alead-in for said anode, an elongated solid metallic cathode positionedopposite and away from said anode and arranged to provide an electricdischarge therebetween, a lead-in for said cathode, a longitudinalelongated hole in said cathode generally in alignment with said anode,the body of said cathode being outside of said envelope with the holeopening into the interior of said envelope, and means for maintaining acooling medium around the body of said cathode, to stabilize thedischarge between the cathode anl anode and to increase the gas densitywithin the hole, including a cooling coil passing around said cathode.

References (Zited by the Examiner UNITED STATES PATENTS 1,912,097 5/33Rinia 313-209 1,914,762 6/33 Thomas 313-213 X 1,932,025 10/33 Thomas313-211 X 1,954,958 4/34 Smythe 313-209 X 2,029,013 1 36 Blackburn313-40 2,087,735 7/37 Pirani 313-42 2,401,059 5/46 Eitel et a1. 313-40 X2,887,603 5/59 Haidinger 313-217 X 2,966,601 12/60 Peek 313-161 X GEORGEN. WESTBY, Primary Examiner.

RALPH G. NILSON, DAVID GALVIN, Examiners.

1. AN ELECTRIC DISCHARGE TUBE INCLUDING AN AIR IMPERVIOUS ENVELOPEFILLED WITH AN INERT GAS AT A PRESSURE BETWEEN 100 MICRONS AND 5 MICRONSOF MERCURY, AN ANODE POSITIONED WITHIN SAID ENVELOPE AND A LEAD-IN FORSAID ANODE, AN ELONGATED SOLID METALLIC CATHODE POSITIONED OPPOSITE ANDAWAY FROM SAID ANODE AND ARRANGED TO PROVIDE AN ELECTRIC DISCHARGETHEREBETWEEN, A LEAD-IN FOR SAID CATHODE, A LONGITUDINAL ELONGATED HOLEIN SAID CATHODE GENERALLY IN ALIGNMENT WITH SAID ANODE, AND MEANS FORSELECTIVELY COOLING SAID CATHODE TO STABILIZE THE DISCHARGE BETWEEN THECATHODE AND ANODE AND TO INCREASE THE GAS DENSITY WITHIN THE HOLE.